I would have her zinc and iron checked to see if she is deficient. Low levels will definitely cause pica. I wouldn't just throw supplements at her unless you know what the problem is because you can cause problems that way as many are toxic in above normal doses. Plus, she could not be absorbing them, so knowing what her blood levels are would be helpful.
Other than that, I have no ideas. My 10 year old is tube fed and it is common to have pica. She mainly eats paper type items like stickers, paper, bandaids, also her feeding tube or anything silicone, and Legos. We have to sort through her Lego block occasionally to make sure she didn't get any little ones in there- minifig hands, heads, and accessories are her favorites. She did have an xray when she was about 4 and we saw that she had also swallowed some coins. Once when hospitalized she chewed a hole into some IV tubing which we didn't discover until we saw that her bed was wet.